Photographic developer solutions can contain undesirably high amounts of silver. Silver lost in effluent streams can present an economic cost as well as an environmental discharge concern. A seasoned photographic developer solution containing silver can also contain sulfite, which can react with silver in a photographic element to increase the amount of silver complex in solution. The silver complex tends to undergo reduction and form silver sludge. Silver sludge is a problem because it can decrease the practical useable lifetime of the developer solution. The silver sludge can foul developer apparatus such as rollers and belts and the like, and consequently foul photographic materials in contact with such apparatus, resulting in poor photographic quality. Silver sludge can also interfere with the flow of developer solution, resulting in poor photographic finish. Silver sludge formation on the developer apparatus and on the walls of the development tanks can necessitate more frequent maintenance and cleaning and result in more down time of the apparatus.
Efforts to minimize silver sludge formation have met with limited success. Some prior art methods employ the addition of mercapto or related compounds to the developer solution to inhibit the formation of silver sludge. A problem with this approach is that such additives can inhibit photographic development and decrease sensitivity. Another problem is that mercapto compounds tend to oxidize, which decreases the silver sludge-inhibiting effects.
Another prior art approach is the use of such mercapto compounds as a component in a photographic emulsion layer. This, however, can result in loss of photographic performance, such as speed and sensitivity loss.
Another prior art approach for recovering silver from a photographic developer solution employs a film having a hydrophilic colloid layer which contains a compound, such as a mercapto compound, capable of adsorbing silver. This can also have the above-noted problems concerning mercapto or related silver adsorbing compounds.
Also known is the use of physical development nuclei (sometimes termed active nuclei), such as Carey Lea Silver, as silver precipitating agents. They can be used to cause silver sludge to settle to the bottom of a development tank. This approach, however, does not result in satisfactorily decreasing, or eliminating, the problem of silver sludge formation.
Another prior art approach is to provide a silver precipitating layer in a photographic element having an image-forming silver halide layer. The silver precipitating layer, which can comprise a hydrophilic colloid containing metal sulfides or colloidal metals, e.g. Carey Lea silver, can decrease the migration of silver or silver halide and lessen silver buildup in a photographic developer solution. A problem with this approach is that silver and silver halide captured in the precipitating layer can impede light transmission and result in decreasing the photographic quality of the exposed film and developed image.
Also known is a processing element comprising a hydrophilic element containing a dispersed silver-precipitating agent, for example a physical development nuclei such as Carey Lea silver. The element is used, however, in a diffusion transfer photographic development process and not for silver recovery from an aqueous solution.